1. Field of the Invention
The present invention relates to an ink jet recording system which is used for outputting hard copies of information such as characters, images or the like in information processing machines such as copying machines, facsimiles, printers, word processors, personal computers and others, and more particularly, to a method and apparatus for recovering ink ejection of a recording head of the ink jet recording system.
2. Description of the Related Art
Ink jet recording apparatuses that perform ink ejection and invalve heat generation are known as types of ink jet recording apparatuses. There are two types of such ink jet apparatuses: one generates thermal energy for ejecting ink, that is, ejects ink by using the thermal energy; and the other incidentally generates heat accompanying the ink ejection. As an example of typical apparatuses of the former type there is known an apparatus that ejects ink on the basis of sudden generation of bubbles accompanying film boiling produced by thermal energy generated by electro-thermal converting elements that operate as ejection energy generating elements. This type of apparatus has advantages as follows: first, a large number of ink orifices and electro-thermal converting elements corresponding thereto can be easily disposed with high density; and second, the ink ejection response to the drive of the electro-thermal converting elements is quick, and hence high speed recording is possible. Thus, this type of apparatuses have been broadly used recently. As the other type of apparatus which incidentally generates heat accompanying the ejection, there is well known as apparatus that uses piezo-electric transducers as ejection energy generating elements. In this system, slight thermal energy is generated when the piezo-electric transducers oscillate for ejecting ink.
In these ink jet recording apparatuses, the thermal energy for or during the ink ejection presents the following problems as already known.
When comparatively high duty recording operations such as recording of visual images or images including solid portions are carried out in such an ink jet recording apparatus, a driving interval of the ejection energy generating elements becomes short. Thus, the next ejection of ink begins before extra heat generated with the ink ejection has been sufficiently dissipated. As a result, heat is stored in ink in ink passages in which ejection energy generating elements are disposed, thereby raising the temperature of the ink. In such a case, fine bubbles remaining in the ink passages will grow owing to the high temperature of the surrounding ink caused by the storing of heat during the recording, or owing to joining of fine bubbles.
The remaining bubbles that grow to a certain size will effect the ejection behavior of ink in the ink passages: they can destabilize the ink ejection by modifying the direction and amount of the ejection. In addition, when such remaining bubbles further grow, they can block the ink passages, thereby hindering the ink ejection. The phenomenon that fine bubbles grow to such sizes as adversely effecting on ink ejection may take place not only by the storing of the heat, but also when the ink jet recording apparatus is left unused for a long time, or when particular orifices are not used for a long time period owing to the arrangement of data to be recorded.
The fine bubbles remaining in the ink passages are produced when the ink therein is raised to a comparatively high temperature by the storing of the heat. In addition, in the apparatus which carries out ink ejection based on abrupt generation of bubbles by using thermal energy, a plurality of fine bubbles that do not serve to for ejection may be generated in conjunction with the bubbles that produce ejection, and may remain in the ink passages. Furthermore, when air is introduced into an ink tube for supplying ink from an ink reservoir to the recording head, the air will form fine bubbles in the ink passages remaining there. The comparatively fine bubbles remaining in the ink passages are partially expelled from the orifices by ink ejection during recording or by an idle ejection operation performed as one of the ejection recovery procedures. Some of the bubbles, however, may grow to a certain size when the heat is stored or when the apparatus is left unused for a long time, and may have an adverse effect on the ink ejection as described above.
To prevent the above-mentioned harmful effects of the remaining bubbles, removal of the remaining bubbles from the ink passages has been conventionally carried out by expelling the ink in the passages as follows: the ink is forcibly sucked through the orifices by using a suction mechanism; or the ink is expelled by exerting pressure on the ink passages with a pressure mechanism.
A comparatively large quantity of ink is expelled by the above-described suction or pressure operation, which can cause the undue consumption of the ink. As a result, the running cost of the recording apparatus increases. Moreover, the suction or pressure carried out during recording will reduce the recording speed of the apparatus because the suction or pressure operation requires comparatively many other operations such as moving the recording head to the capping position in addition to the suction or pressure operation itself.
One characteristic construction of the recording head to be considered in the present invention will be described below in addition to the above-mentioned problem.
The construction is common in recording heads which eject ink by using bubbles generated by the thermal energy. It comprises the following: a substrate that has electro-thermal converting elements that generate thermal energy by applying electric pulses (they are also called "drive pulses" later), electrode wiring for supplying power to the electro-thermal converting elements and so forth formed thereon with the IC fabrication technique; and a top plate that has grooves for forming ink passages in which the electro-thermal converting elements are disposed, and a common liquid chamber for storing ink to be supplied to the ink passages. The substrate and the top plate are joined together by adhesive bonding, thereby constituting the common liquid chamber, ink passages and orifices.
This arrangement of the recording head has some problems concerning the adhesive bonding. First, the adhesives protrude into the ink passages or orifices, which will deviate the shapes of the ink passages or the orifices from the normal shapes, or block the ink passages or orifices. Second, the substrate or the top plate can deform or warp depending on the materials used, which will degrade the adhesive bonding. Third, the substrate and the top plate must be accurately adjusted, which makes complicates the fabricating process of the recording head.
To overcome these problems, Japanese Laid-Open Patent Application No. 2-192954 (or its corresponding European Patent Application Publication No. 0,379,781) propose a recording head which obtains joining force of the substrate and the top plate with a pressure member such as a leaf spring. According to this arrangement, the adhesive can be obviated or limited to a least quantity needed, and hence the deformity of shapes of the ink passages or the orifices owing to the protrusion of the adhesives can be eliminated. Thus, the recording head failure causing the ink ejection failure can be prevented beforehand. Moreover, obviating the adhesives makes the alignment of the substrate and the top plate comparatively easy, thereby simplifying the fabrication process of the recording head.
In the recording head ejecting ink by using thermal energy, the sudden generation of a bubble in the ink, that is, the sudden expansion and the subsequent compression of the bubble, is produced by driving the electro-thermal converting elements. In response to the expansion and compression of the bubble, pressure waves propagate in ink in the ink passages and common liquid chamber. The drive frequency of the electro-thermal converting elements is determined in response to drive data corresponding to characters or images to be recorded, and reaches several kHz in ordinary recording.
When the electro-thermal converting elements are driven for ejecting ink and then the pressure waves of a certain frequency propagate through ink in the passages or the common liquid chamber, periodic forces caused by the pressure waves act on the substrate and the top plate that constitute the ink passages or the chamber.
With regard to this, it has been confirmed that the following phenomenon took place: in the recording head which forms the joining force of the substrate and the top plate with the pressing member such as a leak springs, the oscillation of a certain frequency takes place owing to uneven forces which are caused by the pressure waves and the joining force of the pressing member, and act on the top plate and substrate. Such oscillation, once taking place, produces steady gaps at the rear portions of channel walls each of which separates each of ink passages where the joining force by the pressing member is comparatively small, that is, at the portions behind the electro-thermal converting elements in the ink passages.
Furthermore, the substrate on which the electro-thermal converting elements are disposed has some unevenness because a plurality of layers are overlaid such as a layer for forming the electro-thermal converting elements, a protective layer thereof, or the like. In addition, some portions of the substrate and the top plate can have warped portions. These uneven or wrapped portions can cause thin gaps in the channel walls of the ink passages formed by joining the substrate and the top plate. These gaps will be enlarged by the oscillation mentioned above. Thus, the ink passages will communicate each other through the gaps generated or formed.